1. Field of the Invention
The present invention relates to a radiographic image detector and a radiographic imaging system, and, in particular, to a radiographic image detector used without being connected to an external device at the time of imaging, and to a radiographic imaging system applying such a radiographic image detector.
2. Description of the Related Art
In the field of radiographic imaging for the purpose of medical diagnosis, there has been widely known a radiographic imaging system which irradiates a subject with radiation, detects an intensity distribution of the radiation having transmitted through the subject, and obtains a radiographic image of the subject. Moreover, in recent years, with respect to a radiographic imaging system, there has been developed and used a radiographic image detector called a “flat panel detector” (hereinafter, referred to as “FPD”), which is formed into a thin flat plate having a large number of photoelectric conversion elements arranged thereon in a matrix. The FPD detects the radiation having transmitted through the subject, photoelectrically converts the detected radiation into an electric signal, and performs image processing on the electric signal obtained after photoelectric conversion. It is thus possible to obtain easily and rapidly the radiographic image of the subject.
The radiographic image detector is broadly classified into a stationary detector installed as a part of the system at a predetermined position and a portable (cassette-type) detector freely portable. From a viewpoint of convenience in carriage and easy handling, utilization of the cassette-type radiographic image detector has been widely studied recently.
With respect to the cassette-type radiographic image detector, there has been known one which includes a rechargeable or replaceable internal power supply to drive the radiographic image detector, and is used without being connected to an external device such as an external power supply at the time of imaging. In case of using this kind of radiographic image detector to perform imaging without being connected to an external device, the radiographic image detector can be freely transported and installed depending on the site to perform imaging, and the like. This provides advantages that a degree of freedom in performing the imaging is improved and that it becomes easy to handle the radiographic image detector.
Meanwhile, with the radiographic image detector as described above, it is necessary to transfer radiographic image information acquired through imaging to the external device. Thus, there has been proposed, for example, a radiographic image detector which includes a memory for storing image information and transfers the image information stored in the memory to the external device through a connection terminal (for example, see JP-Tokukaihei-7-140255-A).
Further, in the radiographic image detector to perform imaging operation by using an internal power supply, when the amount of power remained in the internal power supply becomes small, it is necessary, for example, to connect the internal power supply to the external device in order to charge the internal power supply. Therefore, there has been proposed a radiographic image detector which is connected to the external device through a cradle and the like, to be able to charge the internal power supply and perform communication with the external device (for example, see JP-Tokukai-2000-206636-A). Further, there has been proposed a radiographic image detector capable of performing imaging and the like either in a state of being connected to the external device or disconnected therefrom (for example, see JP-Tokukai-2003-172783-A).
However, when imaging is performed without connecting the radiographic image detector to an external device such as the external power supply and with insufficient amount of power remained in the internal power supply, it is sometimes impossible to obtain a suitable image for correct diagnosis. Moreover, when imaging is erroneously performed while a memory to store image information, a communication unit to transmit the image information to the external device, and the like, are not functioning normally, the obtained image may not be stored or transferred to be wasted. In this case, re-imaging of the patient is required, and thus the patient is subjected to unnecessary exposure to radiation, which is unreasonable.